1. Field of the Invention
The present invention relates to particles for a display device and a manufacturing method thereof; a repeatedly rewritable image display medium using the particles for a display device; and an image forming apparatus using the image display medium.
2. Description of the Related Art
A twisting ball display (display by rotation of particles separately colored with two-colors), electrophoretic display, magnetophoretic display, thermal rewritable medium and liquid crystal medium having a memorizing property have been proposed as repeatedly rewritable image display media. While these display technologies are excellent in the memorizing property, there is a problem that a paper-like white display is impossible and the contrast of the medium is low.
On the other hand, Japanese Patent Application Laid-Open (JP-A) No. 2001-312225 has proposed a display technology using a toner for solving the problems above, wherein a conductive colored toner and white particles are enclosed between two electrode substrates opposite each other; a charge is injected into the conductive toner through a charge transporting layer provided on the surface of the electrode at the non-display side substrate; the conductive colored toner in which the charge is injected is transported to the display substrate side located in opposed relation to the non-display substrate by the electric field between the electrode substrates; and the image is displayed by taking advantage of a contrast formed between the conductive colored toner and white particles by allowing the conductive colored toner to adhere to the inner side of the electrode substrate at the display side.
All the image display media are composed of solids in this display technology, which is excellent in that the white color is perfectly switched to the black color in principle (100% switching). However, there are a conductive colored toner not in contact with the charge transport layer provided on the surface of the electrode of the non-display side electrode substrate, and a conductive colored toner isolated from other conductive colored toners in the technology as described above. Such conductive colored toners are randomly distributed in the substrate without being transported by the electric field since no charge has been injected. Accordingly, it is a problem that the contrast of the display is low.
An image display technology taking advantage of an image display medium comprising a pair of substrates; and groups of plural types of particles enclosed between the substrates so as to be movable between the substrates by the applied electric field and having different colors and charging characteristics have been reported in Reports of Japan Hardcopy '99, pp. 249-252.
A high degree of whiteness is obtained by this technology. However, since the particles for an image display used for the image display medium has low fluidity, it was difficult to display an image with a clear contrast.